Historically, deep level mines are commonly cooled by chilled water which is fed gravitationally into the mine, generally through a plurality of pressure drop or energy recovery stations, and again pumped in stages from the mine to the surface. The capital and operating costs involved in pumping energy, pumps, dams, power recovery turbines, large diameter thick-walled piping, in gravitationally braking and pumping the water at a rate of as much as 1.6 tons/second and enormous, particularly in mines as deep as 3000 m or more, where virgin rock temperatures may be between 30 and even up to 90 deg.C. and contribute significantly to mining costs.
A more recent and efficient cooling method consists in feeding ice into the mine in place of chilled water. This method has a advantage over the former methods in that the ice is fed at terminal velocity into the mine through relatively low-pressure piping to suitable ice-water exchangers, but still suffers the disadvantages associated with having to pump water from the mine.